This invention relates to semiconductor devices in general and, more particularly, to a semiconductor isolation processes which may be utilized in the fabrication of CMOS structures.
It is known that CMOS transistors can be fabricated from bulk silicon with conventional techniques to produce devices with high mobilities, low reverse leakage currents, and no latch-up problems at temperatures of operation below 300.degree. C. The aforementioned properties can not be maintained, however, at temperatures above 300.degree. C. Essentially, the problems of latch-up and leakage currents to the well at higher temperatures make it difficult to distinguish between a high state (transistor on) and a low state (transistor off). Accordingly, SIMOX (Separation by Implanted Oxygen) and bond and etch back techniques have been developed to fabricate MOS structures able to operate effectively at higher temperatures. Reference is made, for example, to an article by John B. McKitterick entitled "Very Thin Silicon-On-Insulator Devices For CMOS at 500.degree. C.", pp. 37-41. The primary disadvantages associated with such techniques, however, is that they introduce surface damage due to etching and implantation processes. This surface damage will in turn introduce Qox (oxide charge) during growth of the gate oxide. Qox is detrimental to the overall performance of a CMOS device because it causes drift.
Although various techniques can be utilized to improve the overall quality of the silicon surface, they tend to complicate processing and provide only limited improvement in device performance. As such, it is heretofore been extremely difficult, if not impossible, to fabricate a diverse structure such as a CMOS that can operate to 500.degree. C. with its critical properties preserved.
Accordingly, it is a principal object of the present invention to provide a method of fabricating a CMOS device which will operate at temperatures of up to 500.degree. C. while avoiding the aforementioned problems associated with the prior art.